Geometry in Year 4
Look around the room. Door frames, tabletops, books, window panes — they are all built from straight lines and corners. In Year 4 we learn to describe them: which lines are parallel, which meet at a right angle, and what name a shape gets depending on how its sides and angles fit together.
Three jobs for this year
- Recognise parallel and perpendicular lines — lines that never meet, lines that meet at a right angle.
- Spot the right angle — and tell it apart from an acute or obtuse angle.
- Classify polygons — give a triangle or quadrilateral its proper name (right triangle, square, parallelogram, …).
Words to know
| Word | Meaning |
|---|---|
| line | a straight path that goes on forever in both directions |
| line segment | a piece of a line with two end-points |
| ray | a "half-line" starting at one point and going on forever |
| angle | the opening between two lines meeting at a point |
| polygon | a closed shape made of straight sides |
A line drawn on a sheet of paper is really a segment (the paper ends!), but in school we usually just say "line" to keep things short.
Right angle — the most important angle
A right angle is a quarter turn. It is what you see in:
- the corner of a book
- the corner where two walls meet
- the cross of a window frame
We mark a right angle with a small square inside the corner, like this: ⌐.
Angles smaller than a right angle are acute; angles bigger than a right angle but smaller than half a turn are obtuse.
A first taste of classification
Two shapes with the same number of sides can still get different names depending on which sides are equal and what kind of angles they have.
| Triangle | What makes it special |
|---|---|
| equilateral | all three sides equal |
| isosceles | exactly two sides equal |
| scalene | all three sides different |
| right triangle | one right angle |
| acute triangle | all angles acute |
| obtuse triangle | one obtuse angle |
A triangle can have two names at once: an isosceles right triangle has two equal sides and one right angle. We'll meet quadrilaterals with even more names on their own page.
What you will learn
- Parallel and perpendicular lines — and how we mark them
- Classifying triangles — by sides and by angles
- Classifying quadrilaterals — square, rectangle, rhombus and more
- For parents — practical tips and games